Hydraulic fracturing, also known as “fracking,” is a process for drilling beneath the earth's surface to extract natural gas from shale rock. Once the rock formation is reached, a combination of water, sand and chemicals are inserted into the well to fracture the rock and release gas.
The first step for fracking is to drill and case a well A hole is drilled down vertically and then surface casing is inserted into the hole. Cement is pumped through the casing to seal off the wellbore from fresh water in the earth. After further vertical drilling is completed, a down hole drilling motor is inserted to begin horizontal drilling. When a target distance is reached, production casing is inserted into the full length of the wellbore, and cement is pumped down the casing and out through the hole. Once this step is completed, the hole has been dug and the casing prevents hydrocarbons from seeping out as they are brought to the surface.
The next step is to “perf and frack” the area. “Perfing” is accomplished via a “perforating gun,” which is lowered into the casing. Typically, a plurality of perforating guns, along with corresponding switch subs, are connected to form a gun train. The switch subs include an electronic switch that sends a signal to detonate the corresponding gun. The perf gun is loaded with extremely high explosives. The gun train is lowered by a wireline into the casing, and an electrical current is sent down the hole to set off the explosives in the perf gun. The explosives shoot small holes into the casing and cement. The perf gun explosives can develop a blast pressure on the order of 10 million PSI. The extreme pressures are necessary to overcome both the hydrostatic pressure and the yield pressure of the steel pipe of the perf gun.
After the explosions, the gun train is then pulled from the well. The small holes created by the perf guns provide perforations for the “fracking” stage, which occurs after the gun train is removed.
Finally, the well is “fracked” by sending water, sand and lube into the wellbore under high pressure. The holes in the walls of the well that were blown by the perf gun create channels for this “fracking fluid” to reach the surrounding shale. The extreme pressure causes the shale to fracture, creating a path that allows released gas to flow to the wellbore. Once fracking is complete, a permanent wellhead is installed and a pipeline is constructed to transport the gas.